STEERING CHARACTERISTICS OF SHIPS IN CALM WATER AND WAVES

Hydrodynamic forces and moments due to ship motions in the horizontal plane are obtained at the rotating-arm facility of Davidson Laboratory, in tests of 5-ft Series 60 models. Results are used in computations of ship motions in calm water and waves. A digital computer is used to make nonlinear predictions of ship response to rudder action; these results are compared to trajectories of a free-running model and found to correlate satisfactorily. On the basis of this correlation and by means of the same computation, variations of ship maneuvering motions with changes of ship configuration are examined. The ship-configuration parameters which are varied include rudder size, block coefficient, draft, breadth, profile and section shape. The relationship between maneuvering response and rudder rate is examined, using nonlinear computation, to obtain a basis for determining optimum rudder rate for ships of different speed and size. Computed results show that the minimum rudder rate presently allowed by rules and regulations is reasonable for ocean-trading ships of ordinary size and speed; however, reduced rudder rate may be adequate for very large, relatively slow ships, such as supertankers. A method to predict a ship's yawing motion in following and quartering seas is developed, and variations of ship response with change of wave conditions and ship speed are made clear by means of the computation. Encouraging comparisons are obtained between predicted yawing motions